The present invention relates to an optical cable and more particularly to a cable including a core, having a central element around which at least one coated optical waveguide is stranded, and a cable sheath.
From the German Pat. No. 30 02 498 there is known a communication cable comprising several optical waveguides which each have a primary and a secondary coating and which, together, are stranded about a central element to form a core. Around this stranded core there is placed a retaining helix by which the core is to be held together. Since the retaining helix is seated firmly on the optical waveguides, there is a danger of forces being exerted thereon by which they are mechanically stressed. In order to avoid a deformation of the optical waveguides, the communication cable is filled with a filler which either softens the material of the retaining helix or causes the decomposition thereof, so that the retaining helix exerts forces upon the optical waveguide only during the manufacture of the communication cable.
As is well known, every dielectric waveguide radiates as soon as its axis deviates from a straight line. The radiation is very much dependent on the radius of curvature and, from negligibly small values rapidly increases to losses which are no longer acceptable. In the case of monomode optical waveguides there is still added to this the disadvantageous influence upon the critical wavelengths of modes of different order.
It is the object of the invention to provide an optical cable in which there are not only eliminated the forces coming from the cable structure, but in which also the forces acting from the outside are kept away from the optical waveguides.